1. Field of the Invention
This invention relates to a pointer detection apparatus and a pointer detection method, and more particularly to a pointer detection apparatus and a pointer detection method wherein a pointer is detected by an electrostatic coupling system.
2. Description of the Related Art
Conventionally, for the detection of a position of a pointer used with a touch panel or a like apparatus, various sensor systems have been proposed such as a resistive film system and an electrostatic coupling system (electrostatic capacitive system). In recent years, a pointer detection apparatus incorporating an electrostatic coupling system has been vigorously developed.
Electrostatic coupling systems are divided into two types including a surface capacitive type and a projected capacitive type. An electrostatic coupling system of the surface capacitive type is used, for example, in an ATM (Automated Teller Machine), and that of the projected capacitive type is used, for example, in a portable telephone set. In both systems, a variation of the electrostatic coupling state between a sensor electrode and a pointer, such as a finger or an electrostatic pen, is detected in order to detect a position of the pointer.
A pointer detection apparatus of the projected capacitive electrostatic coupling type includes an electrode formed in a predetermined pattern on a transparent substrate or a transparent film, and detects a variation of the electrostatic coupling state between a pointer and the electrode when the pointer approaches the electrode. Conventionally, for a pointer detection apparatus of this type, various techniques for optimizing the configuration have been proposed and are disclosed, for example, in Japanese Patent Laid-Open Nos. 2003-22158, HEI 9-222947 and HEI 10-161795. In particular, Japanese Patent Laid-Open No. 2003-22158 discloses a technique in which a code division multiplexing system using an orthogonal spread code is applied to a multi-user touch system. Japanese Patent Laid-Open No. HEI 9-222947 discloses a coordinate inputting apparatus which uses a pseudo-random signal. Japanese Patent Laid-Open No. HEI 10-161795 discloses a pen for use with an electrostatic capacitive coordinate apparatus.
Further, a pointer detection apparatus of the type called cross point electrostatic coupling system has been developed from the projected capacitive type electrostatic coupling system. An operation of a pointer detection apparatus of the cross point electrostatic coupling type will now be described briefly with reference to the accompanying drawings. FIG. 84A shows a general configuration of a sensor section and associated elements of a pointer detection apparatus of the cross point electrostatic coupling system and FIG. 84B illustrates an output signal waveform of the pointer detection apparatus.
Referring to FIGS. 84A and 84B, a sensor section 600 includes a transmission conductor array 601 formed from a plurality of transmission conductors 602, and a reception conductor array 603 formed from a plurality of reception conductors 604. An insulating film is formed between the transmission conductor array 601 and the reception conductor array 603. The transmission conductors 602 have a predetermined shape and extend in a predetermined direction, indicated by an arrow mark X in FIG. 84A, and are disposed in parallel to each other and in a spaced relationship by a predetermined distance from each other. The reception conductors 604 have a predetermined shape and extend in a direction crossing the extension direction of the transmission conductors 602, that is, in the direction indicated by an arrow mark Y in FIG. 84A. The reception conductors 604 are disposed in parallel to each other and at a predetermined distance from each other.
In the sensor section 600 having the configuration described above, a predetermined signal is supplied to a predetermined transmission conductor of the transmission conductors 602 and a variation of current flowing to a cross point between the transmission conductor 602 and a reception conductor 604 is detected at each of the cross points of the transmission conductors 602 and the reception conductors 604. When a pointer 610 such as a finger is placed to the sensor section 600, current is shunted through the pointer 610 and thus the current flowing into the reception conductors 604 changes. Therefore, the position of the pointer 610 can be detected by determining a cross point at which current exhibits a variation. Further, with a pointer detection apparatus of the cross point type electrostatic coupling system, simultaneous multipoint detection of a plurality of pointers is possible because a plurality of cross points are formed on the sensor section 600 as seen in FIGS. 84A and 84B.
A principle of position detection of the cross point type electrostatic coupling system will now be described more particularly. Assume for example that a predetermined signal is supplied to the transmission conductor Y6 and a pointing position of the pointer 610, (i.e., a finger) on the transmission conductor Y6 is detected as seen in FIG. 84A. When a signal is supplied to the transmission conductor Y6, the difference between currents flowing to the reception conductors X1 and X2 is detected through a differential amplifier 605. Then, after a predetermined interval of time, the reception conductors to be used for current difference detection are changed over from the reception conductors X1 and X2 to the reception conductors X2 and X3, and the current difference between the reception conductors X2 and X3 is detected. This operation is repeated up to the reception conductor XM.
Thereupon, a level variation of an output signal of the differential amplifier 605 at the position of each cross point on the transmission conductor Y6 is determined. FIG. 84B illustrates a characteristic of the level variation. Referring to FIG. 84B, the illustrated characteristic represents detection signals output from the reception conductors X1 to XM when they are consecutively selected and connected to the differential amplifier 605. A characteristic indicated by a broken line curve in FIG. 84B represents a level variation of the signal output from the differential amplifier 605 and another characteristic indicated by a solid line curve represents a variation of the integration value of the output signal of the differential amplifier 605.
In the example illustrated in FIGS. 84A and 84B, since the pointer 610 is placed in proximity to cross points of the reception conductors X5 and XM−5 on the transmission conductor Y6, the current flowing in proximity to these cross points varies. Therefore, in the example illustrated in FIG. 84B, the output signal of the differential amplifier 605 varies at positions corresponding to positions in proximity to the cross points of the reception conductors X5 and XM−5 on the transmission conductor Y6, and the integration value of the output signal varies. The position of the pointer 610 can be detected based on the variation of the integration value. In a conventional pointer detection apparatus, the detection described above is carried out while successively, one by one, selecting the transmission conductors to be used for the detection.